Over 60 species of Polygonatum grow in the wild in North America, Europe, Asia, Japan and Siberia. Polygonatum is in the lily family, Liliaceae. Some members of this genus have long generation times. For example, Polygonatum cirrhifolium Royle may take 3-5 years to go from seed to seed in the wild.
Polygonatum cirrhifolium Royle is an important medicinal plant of temperate Himalayas (Wealth of India Raw materials, 1976, 9, 365, CSIR, New Delhi). Its rhizomes constitute an important ingredient of Astavarga, a group of eight drugs used extensively in Indian system of medicine mainly as tonics and aphrodisiacs (Misra, B. and Vaishya, R. 1972, Bhavaprakasha Nighantu, pt.1, Chowkhamba Sanskrit Santhan, Sloka 120-122). These attributes arise from the presence of steroidal saponins and polysaccharides in the rhizomatous root-stock of the plant. The plant is also useful in the preparation of cosmetics, skin tonic and as a vegetable (Singh, U. et al., 1983, In: Economic plants of India, IARI, new Delhi, 180). Exploitation of Polygonatum cirrhifolium Royle from wild habitats for its medicinal properties has led to its being placed on the list of threatened species (Shah, N. C. 1983, In: An assessment of threatened plants of India, Botanical Survey of India, Calcutta, 40-49).
According to the seed dormancy classification of Mikolaeva (Mikolaeva, M. G. 1977, In The physiology and biochemistry of seed dormancy and germination, A. A. Khan (ed.), 51-74. North Holland Publ. Co., Amsterdam, N.Y. and oxford), epicotyl dormancy is one of seven types of morphophysiological dormancy.
Morphophysiologically dormant seeds have rudimentary embryos that require cold or some combination of warm or cold stratification to initiate embryo growth (Baskin, J. M. and Baskin, C. C. 1985, Amer. J. Bot., 72(2), 185-290). These requirements can be satisfied or overcome in vitro by providing plant growth regulators and inorganic and organic nutrients together with appropriate thermal and photoperiodic conditions.
Immature embryos can often be induced to germinate by supplying nutrients (Dure, L. S. III, 1975 Ann. Rev. Plant Physiol. 26, 259-278). Such stimulatory effects of gibberillic acids (GA) on germination of both dormant and non-dormant seeds has been widely reported (Lang, A. 1965, 848-893; Stokes, P. 1965, 746-803, Encyclop. Plant Physiology. XV/2; Villiers, T. A. 1972, In: Seed biology (T. T. Kozlowski, ed.) Vol II, 220-281; Black, M. 1980/1981, Israil J. Bot. 29: 181-192).
Gibberillins are known to activate hydrolytic enzymes, especially in darkness. This results in an increase in the osmotic content of the seed, increasing its water potential and giving the hypocotyl power to break through the seed coat. In epicotyl dormancy gibberellins have been found to be potent substitute for the cold stratifications, resulting in the maturation of the embryo.
The literature is replete with references where in vitro approaches have been successfully used to release various forms of physiological dormancy employing various growth enhancing agents, especially gibberillic acid (GA3), 6-benzyl-aminopurine (BAP) and naphthalene acetic acid (NAA). ( Chee, P. P. 1994. Hort Science, 29 (6), 695-97; Nhut, D. T. 1998. Plant Cell Rep., 17(12), 913-16; Choi, Y. E. et al., 1999, Plant Cell Rep., 18(6), 493-99 1994, Hort Science, 29(6), 695-97; Buchheim J. A. T. 1994 Plant Cell Tissue Organ Culture, 36(1), 35-43; Gingas, V. M. and Lineberger, R. B. 1989. Plant Cell Tissue Organ Culture, 17(3), 191-203, Thomas, J. A. and Meyer, M. M. 1987. In vitro 23, 3pt 2, 70 A).
The broader phenological pattern of germination in this particular species was studied under laboratory and field conditions for three years of growth. The seeds of P. cirrhifolium were observed to exhibit epicotyl dormancy and to have separate stratification requirements for hypocotyl, epicotyl and radicle emergence. It was also found that the epicotyl requires one, two or more stratifications to release first foliage leaves. Natural germination of P. cirrhifolium is protracted, meager, and asynchronous. P. cirrhifolium plants take 3 to 5 years to grow to full size when raised from seeds. The inventors are not aware of any published reports where P. cirrhifolium germination has been induced by in vitro or other means.